Sound absorbing wall panels



Feb. 25, 1958 Aw. L. HARTSFIELD 2,824,618

y SOUND ABSORBING WALL PANELS Y Filed July 27, 1956 4 Sheets-Sheet 1 ATTORNEY 1S' Feb. 25, 195s w. l.. HARTSFIELD 2,824,618

SOUND ABSORBING WALL PANELS Filed July 27, 195e 4 Sheets-Sheet 2 ATTORNEYS w. L. HARTsFlELD 2,824,618

souNn mssoRING` WALL PANELs Feb. 25, 195s 4 sheets-Shen 3 Filed July 27, 195s 'Vila/m. Harsfielal ATTORNEY ,5

Feb- 25, 1958 w. L. HARTsFlELD 2,824,618

SOUND ABSORBING WALL PANELS 4 'Sheets-Sheet 4 Filed July 27., 1956 ATTORNEYS United States Patent SOUND ABSDRBING WALL PAELS William L. Hartslield, Washington, D. C.

Application .lilly 27, 1956, Serial No. 600,631

20 Claims. (Cl. 181-33) Another primary object of my invention is to providev an acoustical panel which when assembled with other similar panels will form a composite wall, or even a room, having the above-mentioned absorption characteristics, i. e., nearly complete energy absorption wit nearly negligible reflection within said range.

A further object is the provision of a panel having an. inner or acoustical absorbing face, and having an outer or structural face, said panel effecting a very high degree of attenuation of acoustical energy passing through the: panel from one face to the other, in either direction.

Another object of my invention is to provide a panel including a plurality of adjacent acoustical horns, each horn decreasing in cross-sectional area inwardly `of a composite acoustical absorbing face, in which face thev mouth of each horn lies, and the axis of each horn being: if

curved and disposed at an angle with respect to said composite absorbing face so as to provide the desired acoustical horn length while at the same time providing` a panel of minimum dimensional thickness.

Still another object of my invention is to provide a. I

panel of the type above described wherein each of the curved horns is packed with an acoustical absorbing material, the density of the material being relatively low at; the mouth of the horn and increasing gradually to a. maximum, heavy density, at the small end of the horn.. The lower frequency acoustical energy entering the horn. travels deep thereinto and as it travels encounters everincreasing density of the absorbing material, the density increasing gradually and with no delinite boundary which. might have a tendency to cause reflections of acousticali energy.

A further object of the invention is to provide a panel which is a composite yof the horns comprising it, said horns being so nested that their mouths all lie in the plane of the said acoustical absorbing face of the panel,y and the walls of the horns being delined by sheet material partitions.

Another object of the invention is to provide a panel, the absorbing face of which includes a covering in vthe 'form of a blanket of less-dense absorbing material tov absorb high-frequency waves reaching the said face and to prevent reflection thereof by the outer ends of the sheet material partitions, the blanket being capable of ornamentation to provide an attractive and decorative` appearance when such panels are used as building units.

An additional object of the invention is to provide a panel having a structurally strong outer surface, which surface may be acoustically reflective, and the panel exhibiting strong attenuation to any energy attempting 'lo enter the panel through the structural face and travel through theI panel toward the said absorbing face, this feature being important when constructing a soundproo room.

Yet another object of this invention is to provide a panel which can be readily adapted for use as a door.

Gther objects of the present invention will become apparent during the following discussion of the drawings wherein:

Figure l is a front view oi' a panel looking in the direction cf the sound-absorbing face, various layers of the panel having been broken away to illustrate the underlying construction.

Fig. 2 is a rear view of a panel wherein the rear sheet material comprising the structural face has been partly broken away to show the underlying construction.

Fig. 3 is an enlarged partial cross-sectional view through the panel along the line 3-3 of Fig. l.

Fig. 4 is a still further enlarged partial cross-sectional view through the panel serving to illustrate the manner in which the sound-absorbing material is inserted within the horns which comprise the panel.

Fig. 5 is an exploded view showing the different lengths of the various blankets which comprise the absorbing material packed Within one horn, the blankets respectively being labeled a, b, c, d, e, f, g, l1, i, and j, and corresponding with the blankets shown in Fig. 4 inserted within the uppermost horn.

Fig. 6 is an outside perspective view of a room which might be constructed employing a plurality of the panels which comprise the subject matter of the present in-v vention.

Fig. 7 is an enlarged cross-sectional view along line 77 of Fig. 6.

Fig. 8 is an enlarged cross-sectional view along line E-t of Fig. 6.

Fig. 9 is a front View of a modified form of the panel, various layers of the panel having been broken away to illustrate underlying construction.

Fig. l() is a rear view of the same modified form, wherein the rear sheet material has been partially broken away to show the underlying construction.

Fig. 11 is an enlarged cross-sectional view taken along line l-l of Fig. 9.

As shown in a preferred embodiment in the drawings, Figs. l and 2, each panel comprises a metal box 1 having closed upper and lower ends 1a and having closed right and left sides 1b. The rear of the borl is also enclosed by a sheet material panel 1c and the front of the box may also include a flange 1d serving t e purpose of' reinforcing the box. As best illustrated in Figs. 3 and 4, the inner volume of the box l is divided by means of a plurality of sheet material partitions 2 into a plurality of tapered horns H having relatively large mouths opening in a direction away from the rear panel ic of the box, and each horn H tapering inwardly and, as illustrated, downwardly until the volume of each horn decreases to Zero. Except for the uppermost partition 2., the remaining partitions each has a llange 2a across the end thereof nearest the mouth of the horn, said flanges 2a lending rigidity to the mouths of the horns. lt is to vbe observed, in Fig. 3, that the lowermost horn does not 'actually taper to zero volume but is, in fact, only a relatively small arcuate cavity which does not have as satisfactory characteristics. However, by careful propor- .tioning of the remaining horns within the composite wall panel, the error introduced by the lowermost horn l(marked H in Fig. 3) may be kept to a practical mini-- 1 mum, the horn H being a good absorber of high-frequency energy and presenting only a small area to lowfrequency energy in terms of low frequency wave-lengths.

As best illustrated at the uppermost horn H, in Fig. 4, each of the horns s packed with sound-absorbing material 3, the material preferably used being fiberglass blankets, and blankets of different lengths 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h, 31', and 3j being used so as to obtain graduation of the density of the fiberglass material. Originally, and before packing into a horn, the various blankets 3 are all of the same density, but the lengths thereof are different as shown in Fig. 5. During the construction of the horns, the upper partition 2 is inserted in the box E., and then the Srl-3]' blankets are laid in place on the upper partition. At this time the next lower partition 2 is assembled and is so loaded as to compress the blankets 3er-3j into the shape illustrated in the horn at the upper end of Fig. 4. The process is then repeated by insertion of another group of blankets 3cr-3j on the partition 2 which has been most recently assembled, and so on. it should be apparent that when the padding is assembled in a horn in this manner, the density thereof is altered by compression of the ibreglass blankets 3 rather than by the use of a non-homogeneous material the density of which changes with its length. When all the horns in a wall panel unit have been completed by assembly in this manner, a final ibreglass blanket d is laid over the mouths of all of the horns, as shown in Figs. 3 and 4, and a wire mesh screen 5 or the equivalent is then laid over the fibreglass blanket 4, for the purpose of maintaining the latter in position. The blanket 4 or screen 5 or both could be decorated to provide an ornamental and attractive appearance.

As stated above, the discontinuity at the lowermost horn H' in Fig. 3 is small and, in fact, amounts to a negligible disturbance of the orderly pattern of the panel. This panel is also somewhat different at its upper end where a structural reinforcing member te may be employed to stilfen the top of the box l. The space on either side of the stiffener le is likewise packed with fiberglass of relatively high density, the packing being labeled 6 in the drawings. The purpose of the packing 6 will be hereinafter explained.

Fig. 6 illustrates a soundproof box or room constructed of a plurality of panels 1 each having its soundabsorbing face turned inwardly, and said panels being attached together so as to form a rigid structure.

As is best illustrated in Figs. 7 and 8, when two panels are put together edge-to-edge in a position where they are disposed normal to each other, there results a weak spot in their combined acoustical characteristics, which spot is marked W. Actually, the weak spot W at each junction is merely a line, but it is possible that such a line might leak a considerable amount of energy. It is therefore desirable to employ a pair of angle irons 7' and a for the purpose of strengthening the intersection of the panels, and in addition to pack the voiume in the space immediately outside of the weak spot W with fiberglass material 9 or l0. This fiberglass material should be confined by further sheet metal structure so as to prevent its escape from the vicinity of the weak spot W. Figs. 7 and 8 show two different suitable structures, the one in Fig. 7 being composed of several diagonal panels .il and ila, and the structure in Fig. 8 being rectangular in crosssection and comprising a bent panel StZ-12a.

In View of the fact that it is often as desirable that energy be prevented from entering a room (as shown in Fig. 6) from outside the room as it is desirable to prevent the escape of sound inside of the room to a point outside of the room, I have provided the packing 6 shown at the top of Fig. 3 and also the packing 9 and l@ as shown in Figs. 7 and 8 respectively, so as to attenuate insofar as possible the transfer of sound energy through the panels in either direction.

Figs. 9, and ll show another modified form of the sound absorbing panel, wherein parts which are similar to those in the previous embodiment are labeled with similar reference characters. This modified form also includes a sheet-material box 1 having a rear surface 1c and having sides la and lb surrounded by a flange 1d. The sound absorbing face of the panel is similarly covered by an acoustical blanket 4 held in placeA by an open-mesh screen 5. The modification of structure in this new form lies in the partitions 2G, 21, 22. and 23 which divide the box into a plurality of horns, which, however, are not mutually identical.

These Figures 9l1 illustrate a panel having two nested sets of horns; Fig. ll showing'the left set of horns complete with sound absorbing material 25, which material 25 has been omitted from the right set of horns so as to provide a clearer illustration of the location of the various partitions forming a set of horns. The sound absorbing material 25 may comprise a plurality of blankets of fibreglass graduated in length in a manner analogous to those shown in Fig. 5. The outer edges -of the partitions may be flange-d over in order to stiften them, and the three spaces behind 'the partitions 22 and 23 should be packed full of sound absorbing material 6 so as to attenuate the passage through the panel of sound energy entering through the rear surface lc.

This modified panel is admittedly not as eicient a sound absorber as the preferred embodiment shown in Figs. l through 5, but it still exhibits excellent absorbing characteristics and is more economical to manufacture.

Attenuation characteristics The energy-attenuating characteristics of the present panels vary with the wave length and therefore with the frequency of the incoming energy. The high-frequency energy is relatively easily absorbed and prevented from reflecting and the density of the blanket 4 is about the same as the density of the blankets .3a-3j at the mouths of the horns. High-frequency sound entering through the screen 5 is pretty well absorbed by the blanket 4 and by the less dense portions of the blankets 3ft-3]' in the vicinity of the mouths of the horns, since high-frequency energy does not penetrate very deeply into the horns.

However, as the frequency of the sound entering the panel is reduced, the depth of penetration of the energy into the horns increases. Since it is not practical to manufacture horns having axial lengths anywhere approaching a wave-length of the low-frequency sound energy, the density of the fiberglass material packed into the horns must be increased with depth into the horns.

As stated above, it is extremely undesirable to have abrupt discontinuities in density which may cause reflection of the sounds, and therefore the sound-absorbing material is packed into the horns with gradually increas ing density. Near the innermost ends of the horns the density is so great that the fiberglass becomes virtually impenetrable to the sound energy. Even if low-frequency sound should penetrate deep into the horn and then be reflected outwardly, the energy would still have to travel through a sufficient amount of breglass packing so that it would be substantially entirely absorbed by the time it reached the mouth ofthe horn again.

It is also t-o be noted that because of the angle which the outer portions of the partitions make with respect to any sound wave entering the horn in a direction substantially perpendicular to the plane of the blanket 4, the sound waves reliected from partitions of any horn will tend to be thrown deeper into the horn rather than rellected outwardly in the direction of the blanket d.

I do not limit my invention to the exact form shown in the drawings, for obviously changes may be made within the scope of the following claims.

l claim:

l. An acoustical panel for absorbing vibrational energy reaching the front face of the panel, comprising a frame; a plurality of acoustical horns in said frame, said horns having open mouths all disposed adjacent one another and lying in a common plane parallel to the front face of the panel, and said horns reducing in cross-sectional area rearwardly of the panel; and acoustical absorbing material filling each horn, the density of said material being smoothly graduated from a hard-packed density in the lrlear of each born to a light density near the mouth of each orn.

2. In a panel as set forth in claim 1, an external blanket of light-density acoustical absorbing material across the face of the panel and overlying the mouths of said horns; 1and means for retaining said blanket in place against the orns.

3. An acoustical panel for absorbing vibrational energy reaching the front face of the panel, comprising a box having an open front face, a closed rear face, and closed sides; a plurality of acoustical horns mounted in said box, said horns having open mouths all disposed adjacent one another and lying in a common plane parallel with the front of the box, and said horns reducing in cross-sectional area rearwardly of the panel; and acoustical absorbing material filling each horn, the density of said material being smoothly graduated from a hard-packed density in the rear of each horn to a light density near the mouth of each horn.

4. In a panel as set forth in claim 3, an external blanket of light-density acoustical absorbing material across the lfront face of the panel and overlying the mouths of said orns.

5. In a panel as set forth in claim 4, an open-mesh sheet overlying said external blanket to retain the latter in place, said sheet being attached around its periphery to the sides of the box.

6. In a panel as set forth in claim 3, acoustical absorbing material packed tightly between the horns and the rear and sides of said box to absorb energy entering the box through the rear thereof.

7. An acoustical panel for absorbing vibrational energy reaching the front face of the panel, comprising a box having an open front face, a closed rear face and closed sides; a plurality of partitions each extending from substantially the front face of the box toward the rear face and from one side of the box toward an opposite side to define a plurality of acoustical horns having open mouths lying in a common plane across the front of the box, and said horns reducing in cross-sectional area rearwardly ofthe panel; and acoustical absorbing material filling each horn, the density of said material being smoothly graduated from a hard-packed density in the rear of each horn to a light density near the mouth of each horn.

8. In a panel as set forth in claim 7, an external blanket of light-density acoustical absorbing material across the front face of the panel and overlying the mouths of said horns.

9. In a panel as set forth in claim 8, an open-mesh sheet overlying said external blanket to retain the latter in place, said sheet being attached around its periphery to the sides of the box.

10. In a panel as set forth in claim 7, acoustical absorbing material packed tightly into the spaces within the box lying between the partitions and the rear and sides of the box, said material absorbing energy entering the box through the rear thereof.

11. An acoustical panel for absorbing vibrational energy reaching the front face of the panel, comprising a box having an open front face, a closed rear face and closed sides; a plurality of curved partitions in said box and each disposed substantially normal to the plane of the front face of the box near the front, and extending rearwardly along an offset curve and terminating tangent to said rear face, the partitions each extending from one side of the box toward an opposite side to define a plurality of curved nested acoustical horns having open mouths lying in a common plane parallel to said firstmentioned plane, and said horns reducing in cross-sectional area rearwardly of the panel; and acoustical absorbing material filling each horn.

12. In a panel as set forth in claim 11, an external blanket of light-density acoustical absorbing material across the front face of the panel and overlying the mouths of said horns.

13. In a panel as set forth in claim 12, an open-mesh sheet overlying said external blanket to retain the latter in place, said sheet being attached around its periphery to the sides of the box.

14. In a panel as set forth in claim 1l, acoustical absorbing material packed tightly into the spaces within the box lying between the partitions and the rear and sides of the box, said material absorbing energy entering the box through the rear thereof.

l5. In a panel as set forth in claim 11, the density of said material filling each horn being smoothly graduated from a hard-packed density in the rear of each horn to a light density near the mouth of each horn.

16. In a panel as set forth in claim 15, said material filling each horn comprising a plurality of individual blankets the width of a horn but varying in length, the blankets having their front edges in alignment and their rear edges staggered at different depths in the horn, and the partitions holding the blankets in compression to provide said graduated density.

17. An acoustical panel for absorbing vibrational energy reaching the front face of the panel, comprising a box having an open front face, a closed rear face and closed sides; a plurality of partitions in said box each disposed substantially normal to the plane of the front face of the box near the front and said partitions being dish-shaped and mutually nested in spaced relation, the spacing between adjacent nested partitions decreasing in a direction rearwardly of the front face to form a plurality of tapered horns having open mouths lying n a common plane parallel to said first mentioned plane; and acoustical absorbing material filling each horn.

18. In a panel as set forth in claim 17, an external blanket of light-density acoustical absorbing material across the front face of the panel and overlying the mouths of said horns.

19. In a panel as set forth in claim 17, the density of said material filling each horn being smoothly graduated from a hard-packed density in the rear of each horn to a light density near the mouth of each horn.

20. In a panel as set forth in claim 19, said material filling each horn comprising a plurality of individual blankets the height of a horn but varying in width, the blankets having their front edges in alignment at the mouth of the horn and their rear edges staggered at different depths in the horn, and the partitions holding the blankets in compression to provide said graduated density.

References Cited in the file of this patent UNITED STATES PATENTS 1,972,563 Irvin Sept. 4, 1934 2,087,052 Steuart July 13, 1937 2,278,668 Piety Apr. 7, 1942 2,293,181 Terman Aug. 18, 1942 

